Selective-pole tripping system



Fb 22, 1949. s. L. GOLDSBOROUGH ETAL 7 2,462,180

SELECTIVE-POLE TRIPPING SYSTEM I Filed Nov. 28, 1947 lrc me "2! $2 M WITNESSES: ENVENTORS d l 9 Shirley L Goldsborougiz &

. John L Blaclrbgrn.

flu). v 1 m ATTORNEY Patented Feb. 22, 1949 UNITED STATES PATENT OFFICE SELECTIVE-POLE TRIPPING SYSTEM Application November 28, 1947, Serial No. 788,582

Our invention relates to a selective-pole tripping-system for protecting a three-phase transmission-line against faults by so controlling three single-pole circuit-breakers as to open only a minimum number of breakers, in the phases which are afiected by a fault which involves less than all of the phase-conductors of the line.

Our invention is an improvement over, or a modification of, the selective-pole tripping-system which is described and claimed in the copending Goldsborough application Serial No. 569,181, filed December 21, 1944, in which only one breaker-pole is tripped on a phase-to-phase fault involving no ground-current, as this one breaker-operation is all that is necessary to interrupt the fault-current, According to the NEMA rules, where simultaneous tripping of all faulted poles is not assured, the breakers must have a voltage-rating equal to 115% of the rated circuit-voltage. However, many electric-power customers, who desire to install selective-pole tripping, have their systems already equipped with breakers which are rated at 100% of the rated circuit-voltage, and hence the use of the previously known selective-pole tripping-system, as shown in the copending Goldsborough application, would put these breakers outside of their guaranteed ratings.

The object of our present invention is to provide means for eliminating the single-pole operation on phase-to-phase faults, and obtaining twopole operation, on these particular faults, while retaining the other features of the previous selective-pole tripping-system which is shown in the copending Goldsborough application.

With the foregoing and other objects in View, our invention consists in the circuits, system, apparatus, combinations, parts and methods of operation and use, hereinafter described and claimed, and illustrated in the accompanying drawing, the single figure of which is a very much simplified diagrammatic view of circuits and apparatus, illustrating only those elements and circuit necessary to an understanding of our present invention.

We have illustrated our invention as bein applied to the protection of a three-phase transmission-line I, which is connected to a bus 2 through three single-pole circuit-breakers CBA, CBB and CBC, which are provided with tripcoils TC-A, TCB and TCC, and auxiliary make-contacts aA, a3 and a0, respectively. The several line-phases are distinguished by the letters A, B and C.

As shown in the drawing, we use a distanceresponsive and directionally responsive fault- 3 Claims. (Cl. 175-294) detector panel or box 3, which may be of any desired type, such as that which is shown in the Goldsborough Patent 1,934,662, granted November 7, 1933. It is illustrated as comprising a grounddirectional relay-contact DO, three phase-fault directional-relay contacts DA, DB and DC, three phase-fault distance-relay contacts ZA, ZB and Z0, which are set to have a balance-point for faults just beyond the far end of the protected line-section I, three contactor-switch contacts CSA, CSB and 080 which respond still more sensitively to phase-faults which are further out in the transmission-system, and an overcurrent ground-fault relay IO having one make-contact and three back-contacts. The fault-detector panel 3 is illustrated as being energized from a bank of line-current transformers 4 and from potential-transformers 5.

As shown in the drawing, we also use a phaseselector apparatus or panel 6, which is shown as providing three make-contacts and three backcontacts of three phase-selectors SA, SB and SC for selecting the phase which is involved, in the event of a single line-to-ground fault. These phase-selector relays may be of the construction shown in the Goldsborough Patent 2,320,861, granted June 1, 1943, involving a comparison between the negative and zero phase-sequence components of the line-currents which are supplied to the relays, as by means of a bank of line-current transformers I.

As still further shown in the drawing, we also provide a carrier-current or other pilot-channel protective-relay equipment or panel 8, which is provided with two make-contacts RRG and RRP, one for the ground-fault tripping-circuit, subsequently described, and one for the phase-fault tripping-circuit. This carrier-current fault-detection relaying-equipment may be the distancetype of carrier-current system, such as is shown in the Lenehan et al. Patent 2,255,934, granted September 16, 1941, or the Blackburn et al. Patent 2,367,921, granted January 23, 1945, or a copending Lenehan application, Serial No. 599,832, filed June 16, 1945, now Patent No. 2,449,490, granted September 14, 1948. The carrier-current panel 8 is illustrated as being supplied with current from a set of line-current transformers 9, and voltage from the potential-transformers 5, and it is connected at H to a coupling-transformer l2 which is connected to the phase-C line-conductor C, onthe line-side of a carriercurrent trap 13.

understood that the other line-terminal is, or may be, a duplicate of the terminal equipment which is illustrated. Furthermore, while we have illustrated the several relay-panels 3, 6 and 8 as receiving their line-current energization from three separate banks of line-current transformers 4, l and 9; a single set of line-current transform"- ers could. be used for supplying the relayingcurrents for all three panels.

In the drawing, we also show a very much simplified diagrammatic representation of the essential direct-current tripping-circuits and their associated control-circuits or elements; Incbrief, it may be said that we have added, to the previously known selective-pole. trippingesystem of the copending Goldsboroughapplication- Serial No. 569,181, three auxiliary relays CSA, CSB and CS, and the three back-contacts of the overcurrent ground-fault relay IO.

The several relays are indicated by letter designations orlegends, and the same. letter-designation or legend is appliedto the operating-coil and. to all of the contacts of any given relay. The relays and switches are invariably shown in their open or deenergized positions. The relays for diiierent phases or circuits are distinguished by suitable letters which are sufi'ixed to-the general relay-designation. Arrows are used,v to sym bolically indicate how the various parts of each relay are connected together.

Asshown in thedrawing, there are three tripping-circuits, TA, TB and TC, each oiwhich consis-ts. of its own tripping-coil TC.A, TCB or TCC, asthe case may be, and an auxiliary make-contact of its associated circuit-breaker, as indicated at aA, aB andaC, respectively; The end-terminals of these tripping-circuits TA, TB and TC are connected to the negative relaying.- bus There are two-principalways-for energizing each of these three tripping-circuits TA, TB

andTC, the first way being by way of a groundfault relayingecircuit l5, which connects the car- Bier-current receiver-relay contact REG to the positive relaying-bus and. the second way being by way, of a phase-fault relaying-circuit l6, whichconnects the carrier-current receiver-relay contact RRp-tothe positive bus The ground-fault relaying-circuit llicontinues on, from the receiver-relay Contact RRG,.through the-ground-directional make-contact DO and. the overcurrent ground-relay make-contact. 10, to arelaying-bus l7. From the relaying-bus H, the ground -fault relaying-circuitseparates intov three branches, one for each phase. As the branches are similar, except for the lettering, it will suffice to describe the phase-A. branch, which ener-gize :-v the phase-A tripe-circuit TA through. the phase-selector make-contact SA, the phase-selector back-contact SC, and the contactor-switch back-contact CSB, the latter being shunted by the operating-coil CSX of an. auxiliary relay CSX. This. coilCSXhas such a high resistance that. it does not. permit the flow of an adequate tripping-currentwhcn its bypassing contact CSB isopened. This auxiliary switch CSX has a. make-contact CSX. which joins the other two tripping-circuits TB and TC to each other, for the purpose of securing two-pole tripping in the event of a double phase-to-ground fault, as more.

particularly described and claimed inthe copencling Goldsborough application SerialNo 569,181.

The phase-fault tripping-circuit. l6 containsonly the receiver-rela contact RRP, and is utilized to energize a relaying-bus. l 8,. atwhichpoint the phase-fault relaying-circuit.divides. into three.

4 branches, one for each phase. These branches are again similar, except for the lettering, so that it will suffice to describe the phase-A branch, which energizes the phase-A trip-circuit TA through the phase-fault directional-content DA, the phase-fault impedance contact ZA, and the operating-coil CSA 0f the" auxiliary. relay CSA'. This operating-coil CSA! may have an impedance which is suihciently low to permit the flow of an adequate tripping-current for energizin the phase-A trip-coil TC-A.

In" accordance with our invention, each of the three auxiliary relays CSA', CSB and CS0 has a correspondingly lettered make-contact which x is used to join the trip-circuit of its phase to the trip circuit' of the next lagging phase. Each of these make-contacts, such as CSA, is connected in series with the back-contact of the corresponding auxiliary relay in the next leading phase, such as the CSC back-contact, and in most cases itv islalso-connected in series with one of the backcontacts of the overcurrent ground-fault.- relay IO.

In the operation of our invention, it willbe necessary todescribe only the novel featureswhich. are not shown in the copending. Golder-- borough application Serial No. 569,181.

The novel operation cfour invention takes place upon. the occurrence of an ungrounded phase-tophase iault, which will be assumed to occur from phase-A to phase-B. The phase-A phase-fault relays DA and ZA respond to such afault, and en-- ergize the phase-A tripping-circuit TA through the. carrier-current receiver-relay contact RRP,v

the DA contact, the ZA contact, and the CSA coil- The auxiliary relay GSA responds, and.

connects the phase-A trip-circuit TA to the phase-B trip-circuit TB, through the GSA make. contact, the CSC' back-contact and the IO backcontact. The purpose of the CSC' back-contact is to-prevent the trippin of all three polesv in a casewhere a close-in phase-to-phase fault operates two phase-fault relays, such as DA, ZA,. andDB, ZB. The DB and ZB contacts, in such a case, energize the 0513 relay, whose:make-contact CSB' would energize the TC trip-circuitfrom the TB trip-circuit, except for the presence of the CSA' back-contact inseries with the CSB' make-contact. The purpose of the IQ backcontacts is to break up the circuit throughthe CSA, CS3 and CS0. make-contacts, in the event of faults which involve. ground, so that. our

special two-pole tripping-operation occurs onlyfor phase-faults which do not involve ground.

Whilewe have describedour invention in. only a single. illustrative form of embodiment, which.v

has been: very greatly simplifiedfor facility inillustrating the novel features of the invention, we. wish it to be understood that various changesmay be made, byway of additions, omissions and;

substitutions, without departing from the essentialspirit of our invention. We desire, therefore,- that the appended claimsshall be accorded the broadest construction consistent. with their. lan- We claim as our invention:

1.. Fault-responsive protective. relaying-means for controlling each of a. plurality of single-pole circuitinterrupters in the severalphase-conductors of a three-phase line, comprising a pilot channel. relaying-means for. obtaining a. faultresponsive relay-operation under. the supervision of pilot-channel intelligence received from: the. far end of the protected line-section, groundfault phase-selector means'for obtainingaphaseselecting relay-operation in response to lineconditions obtaining in the event of a single lineto-ground fault, phase-fault phase-selector means for obtaining a phase-selecting relayoperation in response to line-conditions obtaining in the event of a phase-to-phase line-fault, said phase-fault phase-selector means being operative to reliably select only one of the two line-conductors which are involved in some lineto-line faults, ground-fault circuit-interrupter control-circuit means for controlling the selected phase of the single-pole circuit-interrupters in joint response to said pilot-channel relayingmeans and said ground-fault phase-selector means, phase-fault circuit-interrupter controlcircuit means for controlling the selected phase of the single-pole circuit-interrupters in joint response to said pilot-channel relaying-means and said phase-fault phase-selector means, and auxiliary interrupter-controlling circuit-means, associated with said phase-fault circuit-interrupter control-circuit means, for joining the control-circuit selected by a phase-fault selectormeans to the control-circuit for a second linephase, in response to a response of the phasefault phase-selector means for the selected linephase and a non-response of the phase-fault phase-selector means for the third line-phase.

2. Fault-responsive protective relaying-means for controlling each of a plurality of single-pole circuit-interrupters in the several phase-conductors of a three-phase line, comprising a pilotchannel relaying-means for obtaining a faultresponsive relay-operation under the supervision of pilot-channel intelligence received from the a far end of the protected line-section, a groundfault detector-means for responding to the occurrence of a ground-fault, ground-fault phaseselector means for obtaining a phase-selecting relay-operation in response to line-conditions obtaining in the event of a single line-to-ground fault, phase-fault phase-selector means for obtaining a phase-selecting relay-operation in response to line-conditions obtaining in the event of a phase-to-phase line-fault, said phase-fault phase-selector means being operative to reliably select only one of the two line-conductors which are involved in some line-to-line faults, groundfault circuit-interrupter control-circuit means for controlling the selected phase of the singlepole circuit-interrupters in joint response to said pilot-channel relaying-means and said groundfault phase-selector means, phase-fault circuitinterrupter control-circuit means for controlling the selected phase of the single-pole circuitinterrupters in joint response to said pilot-channel relaying-means and said phase-fault phaseselector means, and auxiliary interrupter-controlling circuit-means, associated with said phase-fault circuit-interrupter control-circuit means, for joining the control-circuit selected by a phase-fault selector-means to the control-circuit for a second line-phase, in response to a response of the phase-fault phase-selector means for the selected line-phase, a non-response of the phase-fault phase-selector means for the third line-phase, and an non-response of the ground-fault detector-means.

3. Fault-responsive protective relaying-means for controlling each of a plurality of single-pole circuit-interrupters in the several phase-conductors of a three-phase line, comprising a pilotchannel relaying-means for obtaining a faultresponsive relay-operation under the supervision of pilot-channel intelligence received from the far end of the protected line-section, groundfault phase-selector means for obtaining a phaseselecting relay-operation in response to lineconditions obtaining in the event of a single lineto-ground fault, phase-fault phase-selector means for obtaining a phase-selecting relayoperation in response to line-conditions obtaining in the event of a phase-to-phase line-fault, said phase-fault phase-selector means being operative to select both of the phases which are involved in any phase-to-phase fault, whether grounded or ungrounded, out to a point just beyond the far end of the protected line-section, ground-fault circuit-interrupter control-circuit means for controlling the selected phase of the single-pole circuit-interrupters in joint response to said pilot-channel relaying-means and said ground-fault phase-selector means, and phasefault circuit-interrupter control-circuit means for controlling the selected phases of the singlepole circuit-interrupters in joint response to said pilot-channel relaying-means and said phasefault phase-selector means.

SHIRLEY L. GOLDSBOROUGH. JOHN L. BLACKBURN.

No references cited. 

